This invention relates to leaching of metal sulfides and, more particularly, relates to a method for separating the components of the reaction slurry obtained from leaching of metal sulfides and, still more particularly, relates to a process for the separate recovery of elemental sulfur and residual sulfides and metal salt solution from reaction slurries obtained from leaching of metal sulfides.
It is well known to extract metals from metal sulfides contained in concentrates and ores by reacting the sulfides with such lixiviants as ferric chloride, ferric sulfate, sulfuric acid, hydrochloric acid or nitric acid, often in combinations with oxidizing substances such as air, oxygen, hydrogen peroxide or chlorine whereby metals are dissolved with concurrent oxidation of sulfide sulfur to elemental sulfur. Depending on the lixiviant and the conditions under which the extraction is carried out, certain metals are leached from the sulfides, while other metals are only partly leached or remain unattacked. It is also known that certain metals that are extracted from sulfides may form insoluble compounds. Concentrates or ores invariably contain gangue materials which may be partly dissolved in the extraction or remain unattacked. The extraction of metals from sulfides by leaching with a suitable lixiviant, therefore, generally results in the formation of a leach slurry or reaction slurry which contains dissolved metal, elemental sulfur, unleached sulfides, gangue materials and precipitated compounds.
The separation of the components of the reaction slurry is difficult to achieve. In many cases, unleached sulfides are occluded in elemental sulfur. The elemental sulfur may be present in very finely divided form and any compounds that are precipitated during the extraction are also usually present in very finely divided form. In addition, when the extraction is carried out above the melting point of sulfur, the discharge and the pressure release of the reaction slurry can create problems which may result in the formation of solid sulfur in the amorphous form which is often sticky and difficult to handle.
In conventional treatment of leach reaction slurries, the reaction slurry is normally separated into solids and liquid fractions, usually by thickening, settling or filtration. The solids fraction may be separately treated by flotation to separate unreacted sulfides and elemental sulfur from other solid materials. The flotation concentrate, which contains unreacted sulfides and elemental sulfur, may be further treated by one or a combination of a number of methods to separate unreacted sulfides from elemental sulfur, such as, for example, by pelletization, hot filtration, solvent extraction, or volatilization of the sulfur. Alternatively, the solids fraction may be subjected to a pelletizing operation whereby pellets of sulfur are formed. The sulfur pellets, which may contain occluded sulfides, are separated, melted and the melt is filtered to remove sulfides for recovery of the elemental sulfur.
Solutions obtained from the liquid-solid separation are usually clarified and then subjected to further treatment resulting in the recovery of the desired metals. The conventional treatment of the reaction slurry thus involves many operations, which result in losses and inefficiencies.
It has now been found that the treatment of the reaction slurry obtained from the extraction of metals from metal sulfide ores and concentrates can be much simplified whereby some of the conventionally used process steps are eliminated and whereby losses and inefficiencies are reduced. Thus, the present invention provides a process for the efficient separate recovery of elemental sulfur and dissolved metal from unreacted sulfides, gangue materials and precipitated compounds.